Use of onKeyPreIme

ConstantEditText.java

/**
 * Does not hide the keyboard when back key pressed
 * and perform specified action that provided by Listener.
 */
public class ConstantEditText extends AppCompatEditText {
    
    public interface OnBackKeyListener {
        void onBackKeyPressed();
    }
    
    private OnBackKeyListener onBackKeyListener;
  
    /**
     * Use AtomicBoolean to ensure thread safe.
     */
    private AtomicBoolean onKeyPreImeBlock = new AtomicBoolean(false);
    
    public ConstantEditText(Context context) {
        super(context);
    }
    
    public ConstantEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    
    public ConstantEditText(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    
    
    public OnBackKeyListener getOnBackKeyListener() {
        return onBackKeyListener;
    }
    
    public void setOnBackKeyListener(OnBackKeyListener onBackKeyListener) {
        this.onBackKeyListener = onBackKeyListener;
    }
    
    
    @Override
    public boolean onKeyPreIme(int keyCode, KeyEvent event) {
        if (onKeyPreImeBlock.get())
            return true;
        
        // Ensure that the lines of code below (handling KEYCODE_BACK) execute only once in 100ms
        // So callback should call only once.
        onKeyPreImeBlock.set(true);
        postDelayed(() -> onKeyPreImeBlock.set(false), 100);
        
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            if (onBackKeyListener != null) {
                onBackKeyListener.onBackKeyPressed();
            }
            
            return true;
        }
        
        return super.onKeyPreIme(keyCode, event);
    }
}